This invention relates to a low cost utility winch wherein large ratios are enabled by the winch, e.g., for pulling a 2,000 pound weight, but having fewer parts than is typical for such winches.
A typical heavy duty winch powered by a vehicle battery and for pulling a heavy weight, e.g., to free the vehicle from a stuck condition, includes a series of planetary gear arrangements, e.g., a series of three planetary gear arrangements that reduce the rpms of a motor drive shaft (to thereby increase torque output) on the order of 200 to 1. Each planetary gear arrangement includes a sun gear, a carrier assembly including three planet gears and a ring gear and accordingly in combination, the three planetary gear arrangements collectively require a large number of parts that contribute substantially to the cost of producing the winch.
A less expensive winch to be used for utility applications, i.e., having infrequent use and requiring a lesser pull power, e.g., 2,000 pounds, was developed prior to the present invention to produce the desired gear reduction (on the order of 200 to 1) but with far fewer parts. Such was accomplished using a single planetary gear arrangement. In this prior device, a sun gear is connected directly to the armature shaft of the motor and the sun gear engages three planet gears. The planet gears engage a first ring gear that is non-rotatable. The planet gears axially extend beyond their engagement with the sun gear and the ring gear. A second rotatable ring gear having the same diameter as the first ring gear is placed into engagement with the extended portions of the planet gears. The teeth of one or both ring gears are modified so that one ring gear has fewer teeth than the other, e.g., 70 teeth v. 71 teeth.
To accomplish the above modification, at least one of the ring gears have teeth that do not have an involute inter-engagement with the planets as required for optimum performance. However, there is sufficient mating of the teeth to enable sequential engagement between the teeth of the planets and the teeth of both ring gears. Thus, as the planets are forced to rotate by the sun gear and because the first ring gear is fixed, the planet gears move in a circular pattern relative to the axis of the fixed ring gear. The second ring gear can rotate and with each completed circle of the planets about the ring gear axis, the second ring gear rotates the distance of one tooth, i.e., {fraction (1/70)}th of the circle. The rotatable second ring gear is fixedly mounted to the reel of the winch so that similarly the reel rotates {fraction (1/70)}th of a turn for each full circle of the planets about the axis.
The problem with the above arrangement is that the non-involute or offset meshing of the teeth (between the planets and one of the ring gears) creates undesired noise, loss of efficiency and more rapid wearing of the affected parts. The present invention is also directed to a dual ring gear combination but designed to alleviate the problems of the offset meshing teeth.
The preferred embodiment of the present invention also includes a single planetary gear arrangement. A sun gear (connected to the motor""s drive shaft) drives surrounding planet gears (planets) and the planets are in meshed engagement with a first ring gear. The sun gear, planets and first ring gear are cooperatively configured to provide involute gear teeth inter-engagement. A second ring gear is provided with gear teeth greater in number than the first ring gear, e.g., 71 gear teeth for the second ring gear v. 70 gear teeth for the first ring gear. The planets (three of them) are axially extended beyond the first ring gear and the extended portion is configured to have a greater number of teeth than that portion engaged with the first ring gear, e.g., 27 teeth v. 26 teeth for the portion engaged with the first ring gear. The second ring gear having 71 teeth and the planet gear portions having 27 teeth are cooperatively configured to provide involute inter-engagement and in doing so, the rotatable ring gear is slightly larger in diameter than the first ring gear, as is the extended planet portions larger in diameter than the first planet portions. With the arrangement described, the planets will rotate around their own axis 2.69 times in order for the planets to complete a full circle of movement around the first ring gear axis which is held fixed, i.e., 70÷26. The planets complete a full circle around the second or rotatable ring gear in 2.63 revolutions of the planets, i.e., 71÷27. Thus, the rotatable ring gear is rotated in reverse by about 0.06 of a revolution for every complete revolution of the planets about the first ring gear. Thus the rotatable ring gear rotates in reverse the distance of 1.5 teeth which requires 45 revolutions of the planets to produce a single revolution of the second ring gear.
As a further cost saving feature, the planet gears are rotatably mounted with bearings to provide a desired but limited friction which is overcome by providing a slightly higher powered motor than what would otherwise be required using lower friction bearings. However, the limited resistance to rotation by the planets produces substantial resistance to a force that urges rotation of the second ring gear with the motor inactive (resulting from the high ratio reduction as explained). Thus, the bearing friction produces a highly effective brake and is well within the needs of the weight rating of the utility winches contemplated herein.
A further improvement is provided in the manner of mounting the second ring gear and reel to the motor and gear housing. To enable the desired fit of the clutch ring to the planets without having to critically form the holding bracket for the reel, the attachment of the bracket to the housing of the motor is a sliding interfit. This enables the bracket to be loosely mounted to the housing by a bolt-nut arrangement. It is then adjusted as necessary to obtain the desired fit between the planets and the second ring gear at which point the bolt is tightened.
A further problem that was encountered and resolved is the assembly of the planets to the first ring gear, the planets being fixed at their axes relative to each other by a carrier. The planets as mounted are not symmetrical about the carrier axis (also the ring gear and sun gear axis) and the gears have to be rotatively aligned to fit the ring gears and sun gear. This rotative alignment, upon being established, is replicated for assembly by providing an alignment dot or hole on each planet to be aligned with holes in the carrier.
The above will be more fully appreciated and understood upon reference to the following detailed description having reference therein to the accompanying drawings.